The present invention relates to a dynamic pressure groove processing method for forming the dynamic pressure groove of a fluid dynamic bearing by electrochemical machining.
In regard to a fluid dynamic bearing having a dynamic pressure groove 101 formed by machining as shown in FIG. 3B, if sharp edges 103 and 103 of land portions 102 and 102 located between the dynamic pressure grooves 101 and 101 are brought in contact with the opposite bearing surface (not shown) in an inoperative state, then the bearing surface is damaged, reducing the durability of the bearing. If a surface 102A of the land portion 102 has a significant surface roughness, then the surface 102A of the land portion 102 that has the significant surface roughness comes in contact with the bearing surface in the inoperative state, consequently abrading the bearing surface and reducing the durability of the bearing.
In view of the above, if the dynamic pressure groove is formed by electrochemical machining, as shown in FIG. 3A, then the corners of land portions 82 located between dynamic pressure grooves 81 come to have a curved surface 83, eliminating edges. At the same time, surfaces 82A of the land portions 82 are allowed to have a relatively small surface roughness. Although the abrasion resistance characteristic can be improved with this arrangement, the effects have not been sufficient.
Accordingly, the present invention has the object of providing a dynamic pressure groove processing method capable of improving the abrasion resistance characteristic of the dynamic pressure groove further than that achieved by the conventional electrochemical machining and sufficiently improving the abrasion resistance characteristic and reliability.
In order to achieve the above object, there is provided a dynamic pressure groove processing method comprising the steps of:
setting an electrode tool having an electrode opposite to a workpiece with interposition of a specified gap and forming a dynamic pressure groove on the workpiece by electrochemical machining; and
setting the electrode tool opposite to the workpiece with interposition of a gap larger than the above gap and electrochemically processing a surface of the workpiece.
According to the present invention, first of all, dynamic pressure grooves are formed in specified regions by electrochemical machining with the electrode of an electrode tool put close to a workpiece in the initial stage. According to this electrochemical machining, corners of land portions adjacent to the dynamic pressure groove can be curved and smoothed.
Next, by subjecting the workpiece to electrochemical machining with the electrode of the electrode tool put away from the workpiece, the land portions are to undergo weak electrochemical machining. By this operation, the surface roughness of the surfaces of the land portions can be reduced, and the curved corners of the land portions can be made smoother at the same time.
Therefore, according to the present invention, the surface roughness of the land portions located between the dynamic pressure grooves can be reduced and smoothed further than in the conventional case, allowing the corners of the land portions to be curved more smoothly. Therefore, the abrasion resistance characteristic of the dynamic pressure groove can be improved further than that achieved by the conventional electrochemical machining, allowing the abrasion resistance characteristic and reliability to be sufficiently improved.
Also, there is provided a dynamic pressure groove processing method for setting an electrode tool having an electrode opposite to a workpiece with interposition of a specified gap and forming a dynamic pressure groove on the workpiece by electrochemical machining, whereby
a surface that belongs to the workpiece and is located within a region opposite to an insulator is electrochemically processed more weakly than a surface that belongs to the workpiece and is located within a region opposite to the electrode by flowing a current through the insulator buried in the electrode, the current being smaller than a current to be flowed through the electrode.
According to the present invention, the workpiece located in the region opposite to the electrode of the electrode tool undergoes strong electrochemical machining to have a dynamic pressure groove formed. At the same time, regions that belong to the workpiece and are located in the regions opposite to insulators (corresponding to the land portions) adjacent to the electrode undergo weak electrochemical machining, by which land portions that have a smooth surface and a smoothly curved corner are formed. Therefore, according to the present invention, the surface roughness of the land portions located between the dynamic pressure grooves can be reduced and smoothed further than in the conventional case, allowing the corners of the land portions to be curved more smoothly.